Arc welding

Lore & Background

Arc welding uses a welding power supply to create an electric arc between a metal stick (electrode) and the base material. Power supplies can deliver direct current (DC) or alternating current (AC), and electrodes may be consumable or non-consumable. The welding area is typically protected by shielding gas, vapor, or slag. Processes can be manual, semi-automatic, or fully automated.

Common consumable electrode methods include shielded metal arc welding (SMAW), also known as stick welding, which uses a flux-covered electrode rod; gas metal arc welding (GMAW), which uses a continuously fed wire and shielding gas; flux-cored arc welding (FCAW), which uses a flux-filled tubular wire; and submerged arc welding (SAW), where the arc is struck beneath granular flux. Non-consumable electrode methods include gas tungsten arc welding (GTAW), which uses a tungsten electrode and separate filler material, and plasma arc welding, which uses plasma gas to concentrate the arc.

Power supplies are classified as constant current (used for manual welding) or constant voltage (used for automated welding). Current direction affects penetration and deposition rate: electrode-positive (reversed polarity) generally gives deeper penetration, while electrode-negative (straight polarity) results in faster melt-off. Duty cycle defines safe continuous use within a 10-minute period.

Reader's Guide

Arc welding is significant as a versatile and widely used method for joining metals, with origins in the late 19th century and a major role in shipbuilding during the Second World War. Its legacy continues in the fabrication of steel structures and vehicles. The process encompasses multiple techniques, from manual stick welding to automated submerged arc welding, each suited to different materials and applications. The choice of power supply—constant current or constant voltage—and current polarity affects weld quality, penetration, and deposition rate. Shielding methods protect the weld from atmospheric contamination. Arc welding's adaptability has made it essential in construction, repair, automotive, and marine industries, though some processes require significant operator skill or are limited to certain positions or materials.

Did You Know?

• Arc welding was first developed in the late part of the 19th century and became commercially important in shipbuilding during the Second World War.
• Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding.
• In arc welding, the positively charged anode has a greater heat concentration, around 60%.
• Duty cycle defines the number of minutes within a 10-minute period during which a welder can safely be used; commercial-grade welders typically have a 100% duty cycle.

The Engineering of the Arc — Power, Voltage, and Self-Correction

The power supply sits at the center of every arc welding setup, and the split between constant-current and constant-voltage designs drives most practical choices. In a constant-current arrangement, voltage follows arc length while current dictates heat input. That pairing suits manual methods like gas tungsten arc welding and shielded metal arc welding, where a welder's hand inevitably lets the electrode drift and the arc length wobbles. The supply simply holds amperage steady. Constant-voltage units reverse the logic, fixing voltage and letting current swing, which makes them natural partners for automated processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding. In those systems the wire-to-work gap is held tight: if the wire drifts closer, current surges, heat spikes, the wire tip melts back, and the separation self-corrects. A stick-electrode setup running on constant current typically sits near twenty volts. Duty cycle adds a further constraint, capping how many minutes within a ten-minute window a given welder may run before it must cool down; an eighty-amp machine at a sixty-percent rating needs at least four minutes of rest after six minutes of welding, whereas professional-grade units carry a one-hundred-percent rating.

Polarity — A Small Switch with Big Consequences

Choosing whether the electrode carries a positive or negative charge is far from a trivial toggle. In consumable-electrode processes such as shielded metal arc welding and gas metal arc welding, the positively charged anode concentrates roughly sixty percent of the arc's heat. As a result, DC-plus polarity—electrode positive—delivers deeper penetration and a fuller bead profile, which is why it is the most common stick-welding setting. DC-minus polarity, by contrast, pushes less heat into the workpiece and accelerates the electrode's melt-off rate, a trade-off welders exploit when joining thin sheet metal to avoid burn-through. Non-consumable-electrode methods like gas tungsten arc welding add a third option: alternating current. Because the tungsten electrode only strikes the arc and contributes no filler, a positive electrode yields shallow welds while a negative electrode produces deeper ones. AC flips between the two, landing at a medium penetration. The catch is that the arc must re-ignite after every zero crossing, a weakness engineers have mitigated by designing power units that emit a square-wave pattern instead of a sine wave, eliminating the low-voltage dead time and keeping the arc stable.

Two Philosophies of the Electrode — Stick versus Wire

Shielded metal arc welding, widely known as stick welding, remains one of the most accessible arc processes. A consumable rod, coated in a flux that releases shielding vapors and leaves a protective slag layer, serves simultaneously as electrode and filler. No separate wire feed is needed, equipment stays inexpensive, and operator training can be brief. The trade-offs are real: electrodes must be swapped frequently, slag must be chipped away between passes, and weld speed is comparatively slow. The method is also traditionally confined to ferrous metals, though specialty electrodes now extend it to cast iron, nickel, aluminum, and copper. Gas metal arc welding, or MIG, takes the opposite approach. A continuously fed consumable wire acts as both electrode and filler, while an inert or semi-inert gas flows around it to shield the molten pool. The constant-voltage, direct-current power source most often paired with GMAW enables high welding speeds, but the more complex rig sacrifices the portability and versatility that make stick welding a favorite for repair work and field construction.

From Nineteenth-Century Experiment to Wartime Workhorse

Arc welding traces its origins to the late nineteenth century, when electricity first proved capable of generating enough localized heat to melt and fuse metal. For decades the process remained a laboratory curiosity, but the Second World War transformed it into an industrial linchpin. Shipbuilding yards, desperate to turn out hulls faster than riveting allowed, adopted arc welding on a massive scale, and the technique's commercial importance was cemented in those years. Today the process still underpins the fabrication of steel structures and vehicles, and it spans the full spectrum of operator involvement: fully manual, semi-automatic, and fully automated systems all rely on the same fundamental principle of an electric arc striking between an electrode and the base material. Whether the joint is protected by an inert shielding gas, a flux-derived vapor, or a slag blanket, the goal remains unchanged—melt two pieces of metal together so that, once cooled, they become one.